Scales to classify earthquake intensity

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Earthquake Scales

Richter Scale

The Richter magnitude scale is used to express the level of seismic energy released by an earthquake. Developed in 1935 by Charles F Richter he showed that the more energy an earthquake released the greater the amplitude of the wave detected by a seismograph at a given distance. In other words the size of the peak on the graph along with the distance from the epicentre gives a magnitude reading for the earthquake which will be the same from any location that is able to detect the earthquake.

The Richter scale is logarithmic so each increase of 1 magnitude is actually an increase of ten times the measured amplitude. The scale is limitless but the highest magnitude so far recorded was 9.5 for the Chilean quake of 1960.

Intensity Scale Description Effects
less than 2Micronot felt
2-3Very Minornot felt but recorded
3-4Minoroften felt, no damage
4-5Lightshaking observed
5-6ModerateSome damage
6-7Strongdamaging over a 100 mile area
7-8Majorserious damage over wider area
greater than 8GreatSerious damage over several hundred miles

Modified Mercalli Intensity Scale

A scale developed as a way of measuring the actual effects or intensity of an earthquake at a particular location, and is expressed in roman numerals from I the weakest to XII the strongest.

The intensity scale differs from the Richter scale because the effects of an earthquake depend on location from the epicentre and local geological conditions. Whereas the Richter scale is the measurement of the magnitude of an earthquake independent of location.

Classification Effect description
IInstrumental Detected only by seismographs
IIFeeble Noticed by sensitive people
IIISlight Similar to a passing lorry
IVModerate Loose objects are rocked
VRather strong Felt generally
VIStrong Trees sway, loose objects fall
VIIVery strong Walls crack
VIIIDestructive Chimneys fall; masonry cracks
IXRuinous Houses collapse where ground starts to crack
XDisastrous Ground badly cracked; buildings destroyed
XIVery disastrous Bridges and most buildings destroyed; landslides
XIICatastrophic Ground moves in waves; total destruction

Thanks to a couple of pub quiz users who pointed out errors on this page

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